1. Field of the Invention
The present invention relates to an apparatus for decoding variable length codes, and more particularly to a variable length decoding apparatus capable of achieving a data processing at a low speed and thus usable in high definition televisions (HDTVs).
2. Description of the Prior Art
Generally, there have been known various methods for compressively encoding digital video signals and decoding them. In cases of HDTVs, video motion information is subjected to a discrete cosine transform (DCT), so as to derive its DCT coefficient. The DCT coefficient is quantized and then coded by macroblocks in a variable length coding manner. The obtained variable length code is then sent to a channel. In a receiver device, the variable length code indicative of video information received from the channel is decoded to recover the DCT coefficient. Based on the information expressed by the recovered DCT coefficient, the video is recovered.
Generally, a row of input data is constituted by Y and C coefficients and codes indicative of the characteristics of macroblocks thereof, which have been compressed in a time-division manner. Accordingly, the variable length decoder device which must decode such data should operate at a speed higher than a pixel clock. General HDTVs have a pixel clock of at least 60 MHz. However, there have been known no device enabling a process at a speed higher than such a pixel clock. Therefore, needed is a low speed-processing decoder device capable of processing data at a speed meeting the pixel clock.
Conventionally, such a data processing at a low speed has been achieved, by using a plurality (for example, four or five) of variable length decoders connected in parallel, using an encoding algorithm adapted to adjust the yield of data by the unit of a slice. However, such an arrangement that a plurality of variable length decoders are connected in parallel results in a complex system and an increase in cost. Moreover, an area occupied by the decoder device is increased, thereby resulting in a limitation on compactness.